1. Field of the Invention
The present invention relates generally to providing power to irrigation controllers, and more specifically to conversion of input power signals for use by irrigation controllers.
2. Discussion of the Related Art
Irrigation controllers are typically used to control and actuate valves controlling the flow of water therethrough. Irrigation controllers are often required to be connected to an alternating current (AC) power source. Such controllers often use an input AC power signal at least to generate an output AC power signal used in actuating the valves. For example, a 110/120 or 220/240 volts AC (VAC) (herein generally referred to as 120 and 240 VAC respectively) input AC voltage source is traditionally stepped down or converted into a 24 VAC supply using a conventional step-down transformer. The 24 VAC supply provides suitable power for actuating the various valves controlled by the irrigation controller.
However, there are a number of issues in using the above described step-down power supply. The step-down transformer is constructed to step-down the voltage level of the input voltage (e.g., a primary voltage) to produce a voltage at the output of the transformer (e.g., a secondary voltage). Thus, a first problem with the step-down transformer power supply is that when the voltage level of the power source varies, the input voltage varies, and the step-down transformer produces the output voltage to follow the input voltage. Therefore, the output voltage level will vary in proportion to the input voltage level. This can result in too much or too little operating voltage at the valve solenoid.
Additionally, such transformers used in step-down power supplies must be designed to accommodate for such variations and are typically not very efficient. In some embodiments, these transformers cause excessive heat under load and significant power consumption due to core losses, even when no valves are operating. It is noted that recent governmental regulations are beginning to mandate higher requirements for “standby” power efficiency. These regulations are hard to meet with a conventional step-down transformer.
Another issue with conventional step-down power supplies is that the transformers used are both heavy and expensive. This weight results in added shipping costs and thicker support components. A big additional cost is incurred by the company for the engineering time and activities needed to select and certify new suppliers. Additionally, continuous growth in the global prices for copper increases power transformers' prices. For example, it is believed that over 50% of a transformer's price is derived from copper material costs. This situation hinders long term estimations of cost reductions and future part consolidation programs.
Finally, in order to accommodate the different electrical standards (e.g., 120 and 240 VAC), found in different countries, several different versions of the traditional step-down power supplies and irrigation controllers must be produced using different types of transformers. For example, the transformers must be able to handle the specific voltage (e.g., 120 or 240 VAC) and the specific frequency (e.g., 50 or 60 Hz), as well as normal variations thereof, of the country in which the controller will be used.